Pumping apparatus

ABSTRACT

An improved hydraulic operating mechanism for rocking a beam of a pumping apparatus to reciprocate a well pump disposed in a well pipe and connected to the beam. The operating mechanism includes first and second generally stationary piston rods with first and second stationary pistons thereon, first and second cylinder sections positioned respectively for reciprocating movement relative to the first and second pistons, and means for delivering fluid under pressure to the cylinder sections to drive the cylinder sections relative to the generally stationary piston rods to reciprocate the well pump in such a way that the principal forces placed on the piston rods are tension forces.

United States Patent DH I 14 Claims, 4 Drawing Figs.

U.S. CL...

Field of Search 91/196 F0lb 13/04 103/45,

45PS, 206, 179, 158, 155; 60/52PS;9l/2l6b, 196

[56] References Cited UNITED STATES PATENTS 2432.735 12/1947 Downing60/52X 2,690, i 34 9/1954 Ritchey 103/179 Primary Examiner-Robert M.Walker Att0rneyGreist, Lockwood, Greenawalt and Dewey ABSTRACT: Animproved hydraulic operating mechanism for rocking a beam of a pumpingapparatus to reciprocate a well pump disposed in a well pipe andconnected to the beam. The operating mechanism includes first and secondgenerally stationary piston rods with first and second stationarypistons thereon, first and second cylinder sections positionedrespectively for reciprocating movement relative to the first and secondpistons, and means for delivering fluid under pressure to the cylindersections to drive the cylinder sections relative to the generallystationary piston rods to reciprocate the well pump in such a way thatthe principal forces placed on the piston rods are tension forces.

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I H ll! i IIIII I PATENTEUrtaz IBYI INVENTOR GUNTER MAASSHOFF 4p ATT'YS.W2

PUMPING APPARATUS This invention relates to an oil well pumpingapparatus and more particularly to improvements and innovations in anhydraulic operating mechanism for reciprocating a well pump connected tothe pumping apparatus.

In the recent past, efforts have been made to use an hydraulic operatingmechanism as the driving force for a walking beam of a well pumpapparatus. In one successful mechanism disclosed in U.S. Pat. No.3,369,490, issued to Harry W. Hawk on Feb. 20, 1968, a well pump isconnected to one end of a counterweighted pivoted walking beam and thebeam is rocked about its pivot by an hydraulic operating mechanism whichincludes a cylinder pivotally anchored at its lower end to a base,reciprocating piston rod pivotally connected at its upper to the beam,and a piston received in the cylinder and fixed to the lower end of thepiston rod, Pressurized fluid is alterna'tively delivered to the lowerand upper ends of the cylinder to reciprocate the piston rod in thecylinder. When pressurized fluid is delivered to the upper end of thecylinder to move the piston downwardly, a tension force is placed uponthe piston rod. On the other hand, when pressurized fluid is deliveredto the lower end of the cylinder to extend or move the pistonupwardly,-a compressionforce is placed upon the piston rod.

As is well known, a rod of a given diameter can handle or withstand agreater force in tension than in compression, since a compression forcetends to bend a rod laterally of its longitudinal axis. Consequently,the size of the hydraulic mechanism vdisclosed in the patent referred toabove is determined primarily by the magnitude of the compression offorces which will be placed upon the piston rod. That is to say, themagnitude of the compression forces determines the size of the pistonrod, piston and-cylinder, which, in turn, determine the amount or volumeof fluid needed which, in turn, determines the size of the pump, controlvalves, reservoir and fluid connecting lines for the hydraulic system ofthe pumping apparatus.

Also, there is a smaller volume in the upperportion of the cylinderthrough which the rod extends than in the lower portion. This differencein volume requires more fluid on the upstroke and more force (i.e., toforce fluid from the lower portion of the cylinder) on the down stroke,resulting in an unbalanced loading on the hydraulic system.

To reduce or minimize the size of the hydraulic system, and to balancethe loading on the hydraulic system, the present invention proposes animproved hydraulic operating mechanism wherein only tension forces areplaced upon the piston rod or rods of the mechanism. In other words, apiston rod or rods and a cylinder or cylinders are so arranged andmounted that when the mechanism is operated to rock the walking beam ofthe pumping apparatus only tension forces are imposed upon the pistonrod 'or rods. To accomplish this, a cylinder is pivotally .connected tothe beam and disposed for movement on and relative to a generallystationary piston rod.

In one embodiment of the invention, two cylinder sections are movablymounted, respectively, on two piston rod portions. The cylinder sectionsare pivotally connected to the walking beam while the rod portions areanchored against axial movement, Each rod portion has a piston sectionreceived in one of the cylinder sections. Admission of pressurized fluidto one end of one of the cylinder sections will force that cylinderdownwardly with a tension force being imposed on'the rod portionassociated with that cylinder section, while admission of pressurizedfluid to one end of the other cylinder section will force that cylindersection upwardly with a tension force being imposed on the rod portionassociated with thatcylinder section.

A general object of the invention is to provide an improved hydraulicoperating mechanism for a well pumping apparatus wherein only tensionforces are applied to the piston rods of the mechanism so that the sizeof the piston rods need only be of a diameter sufficient to withstandtension forces to thereby reduce or minimize the size of the hydraulicsystem of the well pumping apparatus.

Another object of the invention is to provide an hydraulic operatingmechanism for a well pumping apparatus wherein the piston rod isanchored at its lower and upper ends. and a cylinder is mounted forreciprocating movement of the piston rod in such a way that the workingportions of the rod experience essentially only tension forces.

A further object of the invention is to provide a symmetrical orbalanced hydraulic operating mechanism where the volume of fluidrequired for the upstroke of the cylinder is essentially equal to thevolume of fluid required for the downstroke of the cylinder.

Additional objects and advantages of this invention will appear from thefollowing description taken in conjunction with the accompanyingdrawings wherein:

FIG. 1 is a side elevational view of a well pumping apparatus embodyingthe principles of this invention;

FIG. 2 is an enlarged vertical sectional view taken along lines 22 ofFIG. 1;

FIG. 3 is a fragmentary view taken along lines 3-3 of FIG. I; and 4 FIG.4 is a fragmentary side elevational view of a modified .form of theinvention shown in FIG. 1. Referring to FIG. I of the drawings, an oilwell pumping apparatus embodying this invention is generally indicatedat 10. Typically the oil well pumping apparatus 10 includes a base 11 onwhich is mounted the bottom end 12!; of a so-called Samson post 12.preferably the post 12 is hollow and serves as a sump or reservoir forthe hydraulic fluid used by the hydraulic operating mechanism of thisinvention. A walking beam 14 is pivotally supported above the base ll atthe top end of the post 12 as indicated at 16. The walking beam M has aforward end 17 mounting a horse head 18 to which a conventional polishrod (not shown) is secured by means of one or more cables 19. The polishrod is connected in an appropriate manner to a well pump in a well pipefor lifting petroleum in a conventional manner during verticalreciprocation of the well pump. Coun- .beam 14 rearwardly of the pivotupport 16 for counterbalancing the forces acting on the forward end ofthe beam 14. As shown, the counterweights 20 are preferably secured bythe cable 21 to a second horse head 22 at the rearward end 24 of thebeam 14. i

In the embodiment of the invention illustrated in FIGS. 1 and 3 a guardframework, generally indicated at 25, is provided for receiving andguiding lthe counterweights 20. Preferably, guard framework 25 includesfour comer posts 25a, 25b, 25c and 25d rigidly secured at their lowerends to the base 11. As shown in FIG. 3, each comer post 25ad has anL-shaped cross section whereby the corner posts 25a-d can be arranged toform comers of a square for receiving square counterweights 20. Asexplained in the patent referred to above, a guard framework or housingis provided for shielding the counterweights from outside forces whichmay disturb or unbalance the forces acting on the-I walking beam, e.g.,for shielding the counterweights from high winds which might shift thecenter of gravity of the counterweights and thereby alter thedisposition of the forces acting on the walking beam. Although theframework 25 is shown as comprising four comer posts 25ad, it is to beunderstood that the guard framework can take different forms, such as anenclosed housing of the type shown in the patent referred to above.Also, it is to be understood that the foregoing arrangement is typicalor conventional and forms no part of the invention.

The improved operating mechanism of the invention, for rocking the beam14 about the pivot support 16, is generally indicated at 26 in FIG. 1.This mechanism 26 includes a piston rod 27 having a first (lower) rod orrod portion 28 and a second (upper) rod or rod portion 29. A firstpiston (or piston section) 30 is mounted at the upper end 28a of thefirst rod 28 and a second piston (or piston section) 31 is mounted atthe lower end 29b of the second rod 29. As shown in FIGS. 1 and 2, thesecond rod 29 is situated above and axially in line with the first rod28 and preferably the pistons 30 and 31 are integral with one another toform a single piston 32 located immediate the upper and lower ends 27aand 27b of the rod 27.

To rigidly secure the rod 27 to the apparatus 10, the lower end 27!) ofthe rod 27 is secured to the base 11 while the upper end 27a of the rod27 is secured to a frame member 34 of the pumping apparatus 10. As shownin FIG. I, one end 340 of the frame member 34 is rigidly fastened to theguard framework 25 which forms one end support for the frame member 34and the other end 34b is rigidly fastened to the Samson post 12 whichforms the other end support for the frame member 34. It is to beunderstood that the rods 28 and 29 need not be integral to form rod 27.Instead, they can be separate parts and, if desired, a small space canexist between pistons 30 and 31.

In the illustrated embodiment, the rod 27 passes through a cylinder 35which is adapted for reciprocal movement on the rod 27 relative to thestationary piston 32. The cylinder 35 includes a first or lower cylindersection 36 which cooperates with the first rod 28 and a second or uppercylinder section 37 which cooperates with the second rod 29. As bestseen in FIG. 2, the upper end 37a of the second cylinder section 37 ispivotally connected to the beam 14 by means of two connecting rods 38and 39. The upper ends 38a and 39a of the connecting rods 38 and 39 arepivotally connected to a shoe 40 which is secured to the underside ofbeam 14. The lower ends 38b and 39b of the connecting rods 38 and 39 arepivotally connected to a bracket 41 which is secured to the upper end37a of the second cylinder section 37.

The pivot connections of the connecting rods 38 and 39 compensate forthe nonlinear movement of the connecting rods as a result of the arcuatemovement of the pivot axis 44 of the pivot connection at the upper ends38a and 39a of the connecting rods 38 and 39. Thus, when the walkingbeam 14 shown in FIG. 1 is rotated counterclockwise, the pivot axis 44will travel an arcuate path as indicated at 45, and the pivotconnections of the connecting rods 38 and 39 permit lateral displacementof the upper ends 38a and 39a of the connecting rods 38 and 39 duringthe arcuate travel of the axis 44.

As illustrated in FIG. 3, the two connecting rods 38 and 39 straddle theframe member 34 and the rod 27. This arrangement of the connecting rods38 and 39 provides: (I) a space or clearance between the connecting rods38 and 39 and the frame member 34 and the rod 27; (2) a direct line offorce from the cylinder 35 to the beam 14 which passes through thevertical axis of the cylinder 35 and the longitudinal horizontal axis ofthe beam 14; and, (3) strong connection between the cylinder 35 and thebeam 14 sufficient to withstand the compression forces placed on theconnecting rods 38 and 39 when the cylinder 35 is moved upwardly.

As best seen in FIG. 3, the frame member 34 is preferably in the form ofa Y to provide a strong structural support for the upper end 27a of therod 27. Accordingly, the frame member 34 has two short arms 46 and 47(forming the end 34a) which are connected at their outer ends to thecorner posts 25a and 25b of the guard framework 25 and a longer arm 48extending from the junction of the three arms 46, 47 and 48 to an outerend (forming the end 34b) which is connected to the Samson post 12. Inthe illustrated embodiment, the short arms 46 and 47 have a generallyL-shaped cross section and the longer arm 48 has an inverted T-shapedcross section to enhance the strength of the frame member 34. It is tobe understood, of course, that the frame member 34 can be formed andconnected in a different manner, so long as the frame member provides anadequate structural support for the rod 27.

As shown in FIG. 1, an hydraulic fluid control system is generallyindicated at 50 and includes a first or lower fluid line 51 coupled orconnected to the lower end 36b of the first cylinder section 36 and asecond or upper fluid line 52 coupled or connected to the upper end 37aof the second cylinder section 37. The first and second fluid lines 51and 52 are also connected to a control mechanism indicated generally at54 in FIG. I, which mechanism 54 includes a control valve of known type.As shown, the control mechanism 54 is mounted on the Samson post 12 andis connected to a reservoir or sump (preferably in the Samson post I2)for the hydraulic fluid used by the hydraulic operating mechanism 26 andto a pump (not shown) which develops the pressurized fluid required. Itis to be understood that the control mechanism 54 can be similar oridentical to the hydraulic control systems shown in FIGS. I or 9 of theHawk patent referred to above. In other words the control mechanism 54can include various fluid lines, check valves, relief valves, etc. ofknown type, and the control mechanism 54 forms no part of thisinvention.

The control valve operates in known manner to alternately deliverpressurized fluid through one of the fluid lines 5| or 52 to one of therespective ends 36b or 37a of the cylinder 35 while fluid is displacedfrom the other end 37a or 36b of the cylinder 35 through the other oneof the fluid lines 52 or 51 and discharged to the reservoir or sump inthe post 12.

The pressurized fluid delivered through the fluid line 51 to thecylinder 35 will act on the lower end of the cylinder 35 and react onthe rod connected side of the piston 30 causing a downstroke of thecylinder 35 to tilt or rock the walking beam 14 counterclockwise asviewed in FIG. 1. Altemately, when pressurized fluid is deliveredthrough the fluid line 52 to the cylinder 35, it will act on the upperend of the cylinder 35 and react on the rod connected side of piston 31causing an upstroke of the cylinder 35, to tilt or rock the walking beam14 clockwise as viewed in FIG. I. With this operation, during thedownstroke and upstroke of the cylinder 35, the main or principal forceimposed on each rod or rod portion 28 and 29 forming rod 27, will be atension force.

Since, only tension forces are imposed upon the rod 27, the rod 27 needonly be of a size (diameter) sufiicient to withstand the tension forcesnecessary to reciprocate the cylinder 35. It is to be understood, that agiven rod will withstand a very much greater force in tension than incompression. Consequently, by allowing only tension forces to be imposedupon the rod 27, a much smaller rod can be utilized than would be thecase if compression forces were also imposed upon the rod 27. As aresult, a smaller cylinder 35 and a smaller piston 32 can be utilizedwhich in turn require a smaller volume of hydraulic fluid. Less fluidreduces the capacity required of the pump, the reservoir, the controlvalves and the fluid lines. Thus, the end result is a smaller, andthereby simpler, hydraulic system of the pumping apparatus 10.

Another advantage of the hydraulic operating mechanism of the presentinvention is that with the rod 27 extending through the cylinder, theupper portion of the mechanism 26 above piston 32 is essentiallysymmetrical to the lower portion below piston 32 such that the volume ofhydraulic fluid used for the upstroke of the cylinder 35 will beessentially the same as for the downstroke of the cylinder 35, therebyproviding a balanced loading on the hydraulic system. Also, the speed ofone stroke can easily be raised or lowered relative to the speed of theother stroke by suitable control means connected to the fluid lines 51and 52.

Although the embodiment of the invention disclosed in FIG. 1 provides avery sturdy operating mechanism by virtue of the connections of theupper and lower ends 27a and 27b of the rod 27 to the rigid frame member34 and the base 11, respectively, the invention can be practiced inother embodiments such as the one shown in FIG. 4. In this modified formof the invention, first and second rods or rod portions 128 and 129 aresituated (generally vertical) on different axes with a first piston 130at the upper free end 128aof the first rod 128 and a second piston 131at the lower free end 12% of the second rod 129. A cylinder means 135 isprovided which includes separate first and second cylinders or cylindersections 136 and 137 disposed respectively for movement on the rods 128and 129. The upper end 136a of the first cylinder 136 is connected to awalking beam at a first point 141 by appropriate linkage 138 (similar toconnecting rods 38 and 39). The upper end 137a of the second cylinder137 is also connected to the walking beam 140 by appropriate linkage 139(also similar to connecting rods 38 and 39), but at a second point 142spaced from the first point l4l. The lower end I28b of the first rod 128is rigidly connected to the base lI while the upper end 129a of thesecond rod 129 is rigidly secured to a structural member I34 of the wellpumping apparatus. This structural member I34 can be a framemember'similar or identical to the frame member 34 shown in FIGS. 1 to3.

A first fluid line 151 is connected to the lower end 1361) of the firstcylinder I36 and, a second fluid line 152 is connected to the upper end1370 of the second cylinder 137.

The operation of the modified form of hydraulic operating mechanism 126shown in FIG. 4 is similar to the operation of the operating mechanism26 shown in FIG. 1. THus, when pressurized fluid is delivered to thelower end 13Gb of the first cylinder 136 via fluid line 151, a forceacting between the rod connected side of the piston I and the lower end136!) of the first cylinder 136 will drive the cylinder 136 downwardlyon the first rod 128 resulting in downward movement of the portion ofthe walking beam 140 shown in FIG. 4. Alternately, when pressurizedfluid is delivered to the upper end 137a of the cylinder 137, a forceacting between the rod connected side of piston 131 and the upper end137a of the second cylinder 137 causes the second cylinder 137 to moveupwardly relative to the second rod 129 resulting in upward movement ofthe portion of the walking beam 140 shown in FIG. 4. When fluid isflowing through the line 151 or 152 to the cylinder 136 or 137, fluid isbeing discharged through the line 152 or 151 from the cylinder 137 or136 to a reservoir (not shown) by virtue of the movement of the piston131 or 130. Also, relief means, such as return lines 161 and 162, may beprovided to relive any fluid or air from the cylinders 136 and 137 whichmight otherwise impede movement of the pistons 130 and 131.

In the operation of the modified form of operating mechanism 126, theprincipal forces imposed upon the rods I28 and 129 are tension forces,and essentially'the same advantages obtained with the operatingmechanism 26 are obtained with the operating mechanism I26.

In the FIG. 4 embodiment, the dimensions of the cylinders 136 and 137(as well as the rod and the piston associated with each cylinder) can bedifferent. Different sized cylinders may be desired where there is asignificant difference between the force needed to move the beam 140clockwise and the force needed to move the beam 140 counterclockwise.

It will be apparent that other modifications and changes can be made inthe foregoing embodiments without departing from the principles of theinvention. For example, the operating mechanism 26 or 126 can besituated between the forward end 17 of the beam 16 and the Samson post12. Therefore, the scope of this invention is to be limited only asrequired by the following claims.

Iclaim:

1. An hydraulic operating mechanism for use in a well pumping apparatuswherein a beam is pivotally supported for rocking movement at a pointabove a base, said mechanism including first and second piston rodssecured against axial movement, with first and second pistons fixedrespectively on said first and second rods, cylinder means includingfirst and second movable cylinder sections which are mounted on saidfirst and second rods respectively and adapted for reciprocatingmovement relative to said first and second rods, means for operativelyconnecting said cylinder means to said beam, and fluid control means fordelivering pressurized fluid to said cylinder sections in such a waythat when the pressurized fluid alternately causes said cylindersections to move relative to said rods to rock said beam about its pivotsupport, the forces imposed upon said rods are mainly tension forces.

2. The operating mechanism of claim I in which said first and secondcylinder sections are separate cylinders and said connecting meansoperatively connects the upper end of said first cylinder to said beamat a first point on said beam and operatively connects the upper end ofsaid second cylinder to said beam at a second point on said beam spacedfrom said first point, and said first rod is spaced away from, andextends along an axis generally parallel to, said second rod.

3. The operating mechanism ofclaim l in which a post having a bottom endand a top end is fixed at said bottom end on said base, said beam beingpivotally supported above said base at the top end of said post, a framemember is rigidly secured at one end to said post, and the upper end ofsaid second rod is connected to said frame member.

4. The operating mechanism of claim I in which counterweights aresupported by and suspended from said beam, a guard framework forreceiving and guiding said counterweights is fixed on said base, a framemember is rigidly secured at one end to said guard framework, and theupper end of said second rod is connected to said frame member.

5. The operating mechanism of claim 1 in which a post having a bottomend and a top end is fixed at said bottom end on said base, said beambeing pivotally supported above said base at said top end of said post,counterweights are supported by and suspended from said beam, a guardframework for receiving and guiding said counterweights is fixed on saidbase at a point spaced from said bottom end of said post, said post andsaid guard framework serving as end supports for a frame member whichhas a first end rigidly secured to said post and a second end rigidlysecured to said guard framework, and the upper end of said second rod isconnected to said frame member.

6. The operating mechanism of claim 5 in which said frame member isgenerally Y-shaped having one long arm extending in one direction forsecurement to one of said end supports and first and second short armsextending in a generally opposite direction for securement to the otherof said end supports.

7. The operating mechanism of claim 6 in which said long arm is rigidlysecured to said post and said first and second short arms are rigidlysecured to said guard framework.

8. Tile operating mechanism of claim 1 in which said first rod and saidsecond rod are situated on the same axis, said first piston beingsituated on said first rod at approximately the upper end thereof andsaid second piston being situated on said second rod at approximatelythe lower end thereof, and the upper end of said first cylinder sectionis connected to the lower end of said second cylinder section to formsaid cylinder means as one integral cylinder which is disposed forsliding and reciprocal movement on said first and second rods.

9. The operating mechanism of claim 8 in which the upper end of saidfirst rod is connected to the lower end of said second rod to form asingle rod, and said first and second pistons are connected together toform a unitary double acting piston.

10. In a well pumping apparatus having a base, a walking beam having aforward end and a rearward end, said forward end of said beam beingadapted to support a well pump, said beam being pivotally supported onsaid base and being adapted to support counterweight means at a pointrearwardly of the pivot support on said base for counterbalancing theforces acting on said forward end of said beam, and a frame memberrigidly fixed to said apparatus and positioned above said base, theimprovement comprising means for rocking said beam including a rodhaving a lower end fixed to said base and an upper end fixed to saidframe member, a piston fixed on said rod at a point between said upperand lower ends of said rod, a cylinder slidably positioned on said rodover said piston and having a closed upper end and a closed lower end,and fluid coupling means connected to the upper and lower ends of saidcylinder for alternately delivering fluid pressure to one end of saidcylinder while fluid is displaced from the other end of said cylinder.

11. The well pumping apparatus of claim 10 in which said means forconnecting said cylinder to said beam includes at least one connectingrod pivotally connected at one end to said beam and pivotally connectedat the other end to said cylinder.

12. The well pumping apparatus of claim 10 in which said means forconnecting said cylinder to said beam includes two connecting rods, eachof said connecting rods having an upper end pivotally connected to saidbeam and a lower end pivotally connected to said cylinder.

13. The well pumping apparatus of claim 12 in which said connecting rodsare positioned to straddle said frame member.

14. In a well pumping apparatus having a base. a beam having a forwardend and a rearward end and being pivotally supported on said base at apoint between said forward end and said rearward end. said forward endof said beam being adapted to support a well pump. said beam also beingadapted to support counterweight means at a point rearwardly of thepivot support on said base for counterbalancing the forces acting onsaid forward end of said beam, and a frame member rigidly fixed to saidapparatus and positioned above said base. the improvement comprisingmeans for rocking said beam including a first rod portion having a lowerend fixed to said base and an upper end situated above said base belowsaid frame member, a first piston section fixed on said first rodportion, a second rod portion having an upper end fixed to said framemember and a lower end situated below said frame member above said base,a second piston section fixed on said second rod portion, cylinder meansincluding first and second cylinder sections, means for connecting saidcylinder means to said beam said first cylinder section being slidablypositioned on said first rod portion with said first piston sectiondisposed in said first cylinder section, said second cylinder sectonbeing slidably positioned on said second rod portion with said secondpiston section disposed in said second cylinder section. first fluidcoupling means connected to said first cylinder section to applypressure against the rod connected side of said first piston section sothat the principal force applied to said first piston rod portion, whenpressurized fluid is delivered to said first cylinder section to movesaid beam in one direction about said pivot support, will be a tensionforce, and second fluid coupling means connected to said second cylindersection for delivering pressurized fluid to said second cylinder sectionto apply pressure against the rod connected side of said second pistonsection so that the principal force applied to said second rod portionwhen pressurized fluid is delivered to said second cylinder section tomove said beam in the opposite direction about said pivot support. willbe a tension force.

1. An hydraulic operating mechanism for use in a well pumping apparatuswherein a beam is pivotally supported for rocking movement at a pointabove a base, said mechanism including first and second piston rodssecured against axial movement, with first and second pistons fixedrespectively on said first and second rods, cylinder means includingfirst and second movable cylinder sections which are mounted on saidfirst and second rods respectively and adapted for reciprocatingmovement relative to said first and second rods, means for operativelyconnecting said cylinder means to said beam, and fluid control means fordelivering pressurized fluid to said cylinder sections in such a waythat when the pressurized fluid alternately causes said cylindersections to move relative to said rods to rock said beam about its pivotsupport, the forces imposed upon said rods are mainly tension forces. 2.The operating mechanism of claim 1 in which said first and secondcylinder sections are separate cylinders and said connecting meansoperatively connects the upper end of said first cylinder to said beamat a first point on said beam and operatively connects the upper end ofsaid second cylinder to said beam at a second point on said beam spacedfrom said first point, and said first rod is spaced away from, andextends along an axis generally parallel to, said second rod.
 3. Theoperating mechanism of claim 1 in which a post having a bottom end and atop end is fixed at said bottom end on said base, said beam beingpivotally supported above said base at the top end of said post, a framemember is rigidly secured at one end to said post, and the upper end ofsaid second rod is connected to said frame member.
 4. The operatingmechanism of claim 1 in which counterweights are supported by andsuspended from said beam, a guard framework for receiving and guidingsaid counterweights is fixed on said base, a frame member is rigidlysecured at one end to said guard framework, and the upper end of saidsecond rod is connected to said frame member.
 5. The operating mechanismof claim 1 in which a post having a bottom end and a top end is fixed atsaid bottom end on said base, said beam being pivotally supported abovesaid base at said top end of said post, counterweights are supported byand suspended from said beam, a guard framework for receiving andguiding said counterweights is fixed on said base at a point spaced fromsaid bottom end of said post, said post and said guard framework servingas end supports for a frame member which has a first end rigidly securedto said post and a second end rigidly secured to said guard framework,and the upper end of said second rod is connected to said frame member.6. The operating mechanism of claim 5 in which said frame member isgenerally Y-shaped having one long arm extending in one direction forsecurement to one of said end supports and first and second short armsextending in a generally opposite direction for securement to the otherof said end supports.
 7. The operating mechanism of claim 6 in whichsaid long arm is rigidly secured to said post and said first and secondshort arms are rigidly secured to said guard framework.
 8. THe operatingmechanism of claim 1 in which said first rod and said second rod aresituated on the same axis, said first piston being situated on saidfirst rod at approximately the upper end thereof and said second pistonbeing situated on said second rod at approximately the lower endthereof, and the upper end of said first cylinder section is connectedto the lower end of said second cylinder section to form said cylindermeans as one integral cylinder which is disposed for sliding andreciprocal movement on said first and second rods.
 9. The operatingmechanism of claim 8 in which the upper end of said first rod isconnected to the lower end of said second rod to form a single rod, andsaid first and second pistons are connected together to form a unitarydouble acting piston.
 10. In a well pumping apparatus having a base, awalking beam having a forward end and a rearward end, said forward endof said beam being adapted to support a well pump, said beam beingpivotally supported on said base and being adapted to supportcounterweight means at a point rearwardly of the pivot support on saidbase for counterbalancing the forces acting on said forward end of saidbeam, and a frame member rigidly fixed to said apparatus and positionedabove said base, the improvement comprising means for rocking said beamincluding a rod having a lower end fixed to said base and an upper endfixed to said frame member, a piston fixed on said rod at a pointbetween said upper and lower ends of said rod, a cylinder slidablypositioned on said rod over said piston and having a closed upper endand a closed lower end, and fluid coupling means connected to the upperand lower ends of said cylinder for alternately delivering fluidpressure to one end of said cylinder while fluid is displaced from theother end of said cylinder.
 11. The well pumping apparatus of claim 10in which said means for connecting said cylinder to said beam includesat least one connecting rod pivotally connected at one end to said beamand pivotally connected at the other end to said cylinder.
 12. The wellpumping apparatus of claim 10 in which said means for connecting saidcylinder to said beam includes two connecting rods, each of saidconnecting rods having an upper end pivotally connected to said beam anda lower end pivotally connected to said cylinder.
 13. The well pumpingapparatus of claim 12 in which said connecting rods are positioned tostraddle said frame member.
 14. In a well pumping apparatus having abase, a beam having a forward end and a rearward end and being pivotallysupported on said base at a point between said forward end and saidrearward end, said forward end of said beam being adapted to support awell pump, said beam also being adapted to support counterweight meansat a point rearwardly of the pivot support on said base forcounterbalancing the forces acting on said forward end of said beam, anda frame member rigidly fixed to said apparatus and positioned above saidbase, the improvement comprising means for rocking said beam including afirst rod portion having a lower end fixed to said base and an upper endsituated above said base below said frame member, a first piston sectionfixed on said first rod portion, a second rod portion having an upperend fixed to said frame member and a lower end situAted below said framemember above said base, a second piston section fixed on said second rodportion, cylinder means including first and second cylinder sections,means for connecting said cylinder means to said beam, said firstcylinder section being slidably positioned on said first rod portionwith said first piston section disposed in said first cylinder section,said second cylinder secton being slidably positioned on said second rodportion with said second piston section disposed in said second cylindersection, first fluid coupling means connected to said first cylindersection to apply pressure against the rod connected side of said firstpiston section so that the principal force applied to said first pistonrod portion, when pressurized fluid is delivered to said first cylindersection to move said beam in one direction about said pivot support,will be a tension force, and second fluid coupling means connected tosaid second cylinder section for delivering pressurized fluid to saidsecond cylinder section to apply pressure against the rod connected sideof said second piston section so that the principal force applied tosaid second rod portion, when pressurized fluid is delivered to saidsecond cylinder section to move said beam in the opposite directionabout said pivot support, will be a tension force.